Patent document 1 proposes a display device displaying different images or contents, each of which is only visible in a specific viewing direction. For instance, an image visible from a right front position is different from an image visible from a left front position. In this display device, individual pixels are alternately used for either one of two windows visible from the right front position and the left front position, respectively; thus, two full-screen-sized windows appear in the screen on the display device. Only a half of all the pixels included in the display device is used for displaying one full-screen-sized window. This naturally degrades a fineness of an image in the window. Further, a view from a central front position is a mixture of images of the two windows.
To prevent degradation of fineness, it is proposed that the full screen region on a display device is divided into two segments, each of which displays only one of two windows. This is disclosed in Patent document 2. Patent document 2 further discloses a viewing angle control, in which a sight line in a specific viewing direction is only allowed to view an image on a window via a micro-prism or cylindrical lens provided to each pixel. Furthermore, another viewing angle control is disclosed which uses an orientation in liquid crystal molecules. The orientation of the molecules is controlled to tilt in a specific direction by applying voltage to a pair of electrodes, between which the molecules interpose.    Patent document 1: JP-2005-84245 A    Patent document 2: JP-2003-15535 A (U.S. Pat. No. 6,954,185)
Technologies disclosed in Patent document 2 involve the following:
(1) In the control using a micro-prism or cylindrical lens to each pixel, a large number of prisms or lenses are required for all the pixels, which complicates a structure of the display device. Each of the micro-prisms or cylindrical lenses needs to be fabricated to maintain a certain degree of accuracy to prevent degradation in fineness of images.
(2) In the control of the orientation of liquid molecules, characteristics of the orientation are significantly varied depending on alignment of substrates sandwiching molecules, which makes it difficult to control the orientation and viewing angle as well.